This invention relates generally to a power steering device for vehicles, mainly automobiles, and more particularly to a power steering device which comprises a pinion shaft connected with the steering wheel, a rack rod which is connected with the steerable wheels and whose rack is in mesh with the pinion of the pinion shaft in the gear box, a power cylinder for hydraulically actuating the rack rod, and a changeover valve for selectively placing the left- and right-hand side hydraulic chambers of the power cylinder into communication with the hydraulic pressure source and the oil reservoir.
In conventional power steering devices of this type a changeover valve called a rotary valve is widely used. The rotary valve requires a plurality of rotary sealing members to ensure that the actuating oil is supplied to the rotating outer sleeve. These rotary sealing members produce a reasonably large frictional resistance against the recovering action of the steering wheel to its neutral position when the steering wheel is steered a very small angle; therefore the conventional devices do not necessarily provide a good steering feeling. Furthermore, the rotary valve becomes necessarily large in size because of its construction and therefore causes difficulties when being assembled into the vehicles.